NSW Australian Consumer Law - Purchased BMW from Dealer - Get a Refund?

This is the first time I've posted here, been looking for help online. Would really appreciate if you could help.

My wife and I moved over to Sydney (from NZ) in December 2015. We purchased a 2006 BMW 120i from a dealer for $12,500. Took it for a test drive, nothing seemed wrong. The dealer was very confident with the car and the cars he sells.
After the first few days, we noticed excessive blue smoke coming from the exhaust, so we contacted him and he said this never happens, took it back to him to get fixed, which he said was a leaky valve and replaced it.

After about a month, the engine light came on and noticed low oil levels. We contacted the dealer again but this time, he was very reluctant to repair the vehicle, saying he can't fix it which we knew was rubbish, so after telling him we will take it further he came round and said he will fix it.

We had taken the car to a BMW mechanic to check what the engine light was for (at our own expense), they said us for oxygen sensor and leaking gasket.

Told the dealer and he agreed to fix it which he did.

Now it has only been one week since he fixed it and the oil light came back on and a large amount of blue smoke coming from the exhaust. So again, for the third time, we have contacted him, he has agreed to get his mechanic to look at it, but can't guarantee he can fix it. He told us that BMW's eat oil like this all the time (I have text messages to prove this) and that he has a BMW 3 series that does this too, making it seem like it's a normal thing which it isn't.

If we had known this car was going to be blowing out blue smoke / leaking and consuming oil and having other issues, we would not have brought it, which from my understanding is what is considered a major problem.